Many communication terminals, such as cellular communication terminals, cellular phones, smart watches, tablet computers, laptop computers, and data terminals, are now equipped with Global Network Satellite System (GNSS) receivers to enable users to determine their location. GPS is a space-based radio trilateration system using a constellation of satellites in orbit around the Earth. A GNSS receiver trilaterates its position based on timing of radio signals it receives from various ones of the satellites and the known location of those satellites. Example GNSS systems include Global Positioning System (GPS), Global Orbiting Navigation Satellite System (GLONASS), and Galileo.
Determining the position of a GNSS receiver typically requires the acquisition of a set of navigational parameters from the navigational data signals of four or more GNSS satellites. The algorithms that are used to acquire GNSS signals and determine position therefrom are typically complex and may require substantial processing throughput. The process of monitoring GNSS signals can be significantly affected by environmental factors. For example, GNSS signals that may be easily acquired in the open typically become harder or impossible to acquire when a receiver terminal is within a building.
Location determination systems used for emergency calling have been determined in some circumstances to fail during more than 50% of e911 calls originated from terminals inside buildings. The Federal Communications Commission (FCC) in the United States has therefore asked the telecommunications industry to provide improved terrestrial positioning systems. New proposed positioning systems include Terrestrial Beacon Systems system that uses powerful terrestrially-based transmitters to transmit very precise timed signal and information over a GNSS-like channel about the geographic location of the transmitters. However, these systems will require significant investment to deploy new infrastructure.